1. Field of the Disclosure
The present disclosure relates to a double gate type thin film transistor, and more particularly, to a double gate type thin film transistor including a second gate electrode that is semi-transparent to prevent inflow of light into the transistor and an organic light emitting diode display device including the same.
2. Discussion of the Related Art
Recently, with the advent of an information-oriented society, the field of display devices configured to process and display a large amount of information has rapidly been developed. In particular, liquid crystal displays (LCDs) or organic light emitting diode (OLED) displays have lately been developed as flat panel displays (FPDs) having excellent performance, such as a small thickness, light weight, and low power consumption, and has superseded conventional cathode-ray tubes (CRTs).
Among the FPDs, the OLED display is widely used because it has advantages, such as light weight, thin profile, and low power consumption. The OLED display is used for various devices, such as laptop computer, monitor, and television.
Recently, as a driving or switching element for the display, an amorphous silicon thin film transistor (TFT) is usually used. However, as the display becomes large in size and requires high quality, an element having high performance is required. Accordingly, a TFT having high performance, such as high mobility, and a method of manufacturing the same is required.
Since a poly silicon TFT has high mobility, it can be applied to a display of high quality. However, complicated processes are required to form the poly silicon TFT, and production cost increases.
Accordingly, a new type TFT is required that has advantages of both the amorphous silicon TFT and the poly silicon TFT, and oxide TFTs are suggested.
There is a ZnO-based TFT among the oxide TFTs. Recently, as ZnO-based materials, Zn oxide material, GaInZn oxide material and etc. are provided. Since the ZnO-based TFT is able to be manufactured at low temperature and is in amorphous state, there is advantage that a large-sized display can be manufactured. Further, the ZnO-based TFT has high mobility and thus has an excellent electric property like the poly silicon TFT.
FIG. 1 is a cross-sectional view illustrating a bottom gate type TFT according to the related art.
Referring to FIG. 1, the TFT 1 includes a gate electrode 20 on a substrate 10, a gate insulating layer 30 on the gate electrode 20, an oxide semiconductor layer 40 on the gate insulating layer 30, and source and drain electrodes 60 and 70 on the oxide semiconductor layer 40.
The TFT 1 is a usual bottom type TFT, and in order to prevent light preventing flowing into the TFT, used is a method that prevents light from inflowing from a bottom side of the gate electrode 20 with the gate electrode increasing in size.
However, in this method, it is difficult to block inflow of light from a top side, aperture ratio is reduced, and a RC delay increases due to a parasitic capacitance between the source and drain electrodes and the gate electrode.